Triumph Repair/no spark


QUESTION: Howard.. I have a 1979 TR7 with a 45DM distributor #41812 and a AB14 amplifier #47283  I have just rebuilt the motor and advanced distributor has rebuilt he distributor.. I have the wiring schematic to wire the coil. This was in the car before i removed the motor and it ran the last time it was started.. (eight yrs ago) I located all the wires and assembled it according to the schematic. I still have no spark. Can you help me check the voltage i should have at different points. It is a new coil also. I get 12 volts with the ignition on..from the positive side of the coil to ground but i get zero volts from the positive side to negative side.. What else can i check or do i have a problem already. How do I check the AB14 amplifier.. Thank you in advance..

ANSWER: Hi Michael,

I can't find any reference to your part mumbers but after 36 years since the car was new that don't mean anything because the distributor could have been replaced several times. The original system was an Opus/Lucas ignition system. It used a 6v coil and a resistor wire to power the coil in the "ON" position, but used a straight 12v from the starter solenoid to direct power the coil in the "Start" position. The "Amp" was mounted on the distributor with the vacuum unit mounted on the "Amp". The pick-up inside was straight wired to the "Amp" with no plug. The "Amp" was powered by a external ballast resistor.

We all dredded the Opus/Lucas system as they often failed more then once even while in waranty (only one year) This prompted many aftermarket systems to be built. Petronix and even Mallory jumped on the band wagon. There was even an LED system to replace the Opus/Lucas system.

The only tests we had was to ohm the coil (or we use to just remove the (-) wire off the coil and take a jumper and connect it to the (-) terminal of the coil and remove the coil wire from the cap and hold it about a 1/4 inch from a ground and scratch the jumper on a ground while the key was "ON".) If it jumped a good thick blue spark then the wiring to the coil and the coil was OK. Then we checked the air gap in the pick-up (about .012", if I remember correctly) And checked power to the ballast resistor (Amp drive resistor) with the key "ON" and power out of the resistor.

A (short-cut test) we used was to put a volt meter on the (-) side of the coil and spin the starter. All ignition coils have to be grounded by either points or electrically grounded by electronic ignition systems then open circuited to operate the coil. If we didn't see the pulsing power and grounding of the (-) side of the coil as the starter spun the engine we just replaced the Opus/Lucas unit as it failed so often.

That is about all we could test. The system etiher worked or it didn't and we had no good test of the "Amp" or it's attached Pick-up. It is always a shock for me to see any Opus/Lucas system still operating on any of the British cars it was installed on.

I have had several TR-7s and loved the car but got tired of replacing the electronic ignition systems in them and the one TR-7 I still own I tossed the electronic ignition system and installed an old MG midget distributor shaft with a points cam and put points in it.

Many electronic ignition systems don't have a safety diod in them to bleed off a high voltage spike and even if a plug wire were to jump off, a spark will run down the coil tower to the (-) terminal of the coil and on to the Amp and destroy it instantly.


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QUESTION: This is a link to the distributor and amplifier that i have installed on my car. It was replaced since it was new. The car started when it was left in storage. How do i check to see if the ampflier is working properly?

That Amp looks like a typical Jaguar Amp. The actual Amp is the 4 pin unit inside the aluminum box and is a GM Amp that can be bought at any auto parts store for about $35.00

It is good to see they put a Zener Diod in it to protect the Amp from a spark that will jump down the coil tower if a plug wire comes off.

I have no test procedure for a GM Amp. If you connected the white wire to the ignition power and made sure the Amp was grounded like it said to do and you checked the air gap at the reluctor to about .012" then it should operate. If not you need to contact the people you bought the unit from. Since the pick-up is a separate unit not like the original system, then you can unplug it from the Amp and check across the two pins with an ohm meter. That is a coil type pick-up so all you need to see is a connection with some resistance between the two pins and no connection to ground.

The diod can be tested with a ohm meter and after grounding the wire on the condenser to bleed off any charge it might have you can check it also with a ohm meter to see that it is not shorted but you can't test it for it's function with an ohm meter. It is a condenser.

If you don't have any contact with the people you bought the unit from you can remove the GM modual from the box and take it to an auto parts store and ask if they can test the GM unit off of a car. If they ask what GM it came off of, tell them you don't know and ask if they can cross the GM number on the unit. I replaced several units that way for $35. instead of paying the $300 to $400 Jaguar wanted for it.


Triumph Repair

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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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